Fuel cells are electrochemical cells in which a free energy change resulting from a fuel oxidation reaction is converted into electrical energy. As shown in FIG. 1, a typical fuel cell 10 consists of a fuel electrode (anode) 12 and an oxidant electrode (cathode) 14, separated by an ion-conducting electrolyte 16. The electrodes are connected electrically to a load (such as an electronic circuit) 18 by an external circuit conductor. In the circuit conductor, electric current is transported by the flow of electrons, whereas in the electrolyte it is transported by the flow of ions, such as the hydrogen ion (H.sup.+) in acid electrolytes, or the hydroxyl ion (OH.sup.-) in alkaline electrolytes. In theory, any substance capable of chemical oxidation that can be supplied continuously (as a gas or fluid) can be oxidized galvanically as the fuel at the anode 12 of a fuel cell. Similarly, the oxidant can be any material that can be reduced at a sufficient rate. Gaseous hydrogen has become the fuel of choice for most applications, because of its high reactivity in the presence of suitable catalysts and because of its high energy density. Similarly, at the fuel cell cathode 14 the most common oxidant is gaseous oxygen, which is readily and economically available from the air for fuel cells used in terrestrial applications. When gaseous hydrogen and oxygen are used as fuel and oxidant, the electrodes are porous to permit the gas-electrolyte junction to be as great as possible. The electrodes must be electronic conductors, and possess the appropriate reactivity to give significant reaction rates. At the anode 12, incoming hydrogen gas ionizes to produce hydrogen ions and electrons. Since the electrolyte is a non-electronic conductor, the electrons flow away from the anode via the metallic external circuit 18. At the cathode 14, oxygen gas reacts with the hydrogen ions migrating through the electrolyte 16 and the incoming electrons from the external circuit to produce water as a byproduct. The byproduct water is typically extracted as vapor. The overall reaction that takes place in the fuel cell is the sum of the anode and cathode reactions, with part of the free energy of reaction released directly as electrical energy. The difference between this available free energy and the heat of reaction is produced as heat at the temperature of the fuel cell. It can be seen that as long as hydrogen and oxygen are fed to the fuel cell, the flow of electric current will be sustained by electronic flow in the external circuit and ionic flow in the electrolyte.
In practice, a number of these unit fuel cells are normally stacked or `ganged` together to form a fuel cell assembly. A number of individual cells are electrically connected in series by abutting the anode current collector of one cell with the cathode current collector of its nearest neighbor in the stack. Fuel and oxidant are introduced through manifolds into respective chambers. The dilemma with stacking and porting these traditional types of fuel cells lies in the extremely complex flat stack arrangements and numerous parts (membranes, gaskets, channels, electrodes and bipolar plates) that are difficult and expensive to fabricate and assemble, and are highly subject to catastrophic failure of the entire system if a leak develops. As can be easily appreciated, the cost of fabricating and assembling fuel cells is significant, due to the materials and labor involved. In addition, it is difficult to transport the oxygen and hydrogen through the stack, and increased gas transport requires pressurization, with attendant difficulties.
An alternate style of fuel cell has been recently proposed (U.S. Pat. No. 5,783,324) which is a side-by-side configuration in which a number of individual cells are placed next to each other in a planar arrangement. This is an elegant solution to the problem of gas transport and mechanical hardware. However, in order to connect the individual cells together, an electric connection must pass through the plane of the cell to the adjacent cell (see, for example, U.S. Pat. Nos. 5,190,834 and 5,783,324). These solutions have a major flaw, in that the electrical connection that traverses the electrolyte needs to be sealed and is prone to failure over the life of the cell. Thus, although planar fuel cells continue to hold technological promise, they remain a dream that has so far proven to be elusive to the skilled artisan. An improved planar fuel cell that is less complex and less prone to failure would be a significant addition to the field.